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Non-Culture Blood Test Proves Mettle in ID’ing Bloodstream Infections

The T2Bacteria Panel, a non-culture diagnostic test that identifies pathogens in whole blood samples, showed high levels of sensitivity and specificity for detecting bloodstream infections, a newly published multicenter study found.

The diagnostic test had a per-patient sensitivity for proven blood stream infections of 90% (95% CI 76%-96%) and a specificity of 90% (95% CI 88%-91%), reported M. Hong Nguyen, MD, of the University of Pittsburgh School of Medicine, and colleagues, writing in Annals of Internal Medicine.

T2Bacteria and T2Candida panels, marketed by T2Biosystems, are the sole blood culture-free diagnostic tests to receive market clearance from the FDA. The T2 Bacteria Panel identifies the five most common ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Escherichia coli) pathogens, the authors said.

“Now that performance characteristics of both panels have been established in multicenter clinical trials, a top priority is to define their precise roles in clinical practice and their effect on patient outcomes,” they wrote.

But in an editorial published with the study, David A Weinrib, MD, and Gerald A. Capraro, PhD, of Atrium Health, Charlotte, North Carolina, wrote that it remains to be seen if the T2Bacteria Panel “adds value to the management of patients with suspected [bloodstream infection] or sepsis.”

They called for patient outcome studies to “determine the T2Bacteria Panel’s place in modern [antibiotic] stewardship and patient care.”

“Can studies demonstrate better outcomes, such as significantly shorter time to appropriate therapy, compared with use of multiplex PCR or positive blood cultures and other standards of care?” the editorialists wrote. “Does the test improve 30-day survival, decrease length of stay or reduce the number of days of antibiotic therapy per 1,000 patient days? If the yield is low in undifferentiated patients with fever, does a subset of hemodynamically unstable patients stand to benefit from this assay?”

The prospective, multicenter study by Nguyen and colleagues involved 1,427 adult patients with suspected bloodstream infection or sepsis receiving treatment at 11 U.S. hospitals.

Blood cultures were ordered as standard of care in all patients, and the performance of the T2Bacteria Panel was compared to blood culture for the diagnosis of confirmed or possible bloodstream infections caused by the bacteria targeted by the panel.

Among the main study findings:

  • The T2Bacteria Panel was positive for targeted bacteria in 13% of patients (181 of 1,427), compared to 3% (39 of 1,427) for blood culture
  • Depending on the number of samples tested, the mean times for identifying targeted pathogens were 3.61 (SD, 0.2) to 7.70 (SD, 1.38) hours for the T2Bacteria Panel, versus 38.5 (SD, 32.8) and 71.7 (SD, 39.3) hours for blood culture
  • Negative predictive value of the T2Bacteria Panel was 99.7%
  • 10% of patients (146 of 1,427) had negative blood cultures and positive T2Bacteria results, and 60% of these (88 of 146) were associated with probable (n=62) or possible (n=26) BSIs, based on a composite of clinical findings, other blood culture results, or non-blood cultures

“In 78% of probable or possible BSIs, patients had negative blood cultures and positive T2Bacteria results despite treatment with active antibiotics,” the researchers wrote, noting that only 20% of patients with positive blood cultures and T2Bacteria results were receiving antibiotics.

“Therefore, T2Bacteria may have particular value over blood cultures in patients who are already receiving antimicrobial therapy,” they added.

Nguyen and colleagues concluded that T2Bacteria, “will most likely be useful if it is used in conjunction with blood and non-blood cultures and results are interpreted with careful consideration of patients’ clinical status and antibiotic use.”

But Weinrib and Capraro expressed concern about the impact of the wide use of the T2Bacteria Panel on laboratory workflow, given that culture will still be required.

“Personnel, space, and efficiency are important issues that must be addressed, especially when adding testing that does not have proven clinical benefit in being considered,” the editorialists wrote. “Hospitals that have moved most microbiological testing off campus would need to perform this test on site to realize decreased time to the results.”

This research was funded by T2 Biosystems.

Lead researcher M. Hong Nguyen reported no disclosures. Researcher Cornelius Clancy reported financial support from T2 Biosystems. Researcher Bryan Schmitt reported nonfinancial support from T2 Biosystems and personal fees from the company outside the submitted work. Other researchers reported grants, as well as financial and non-financial support received from other pharmaceutical companies.